In no man’s land, dogs did jobs humans could not, such as taking supplies to the wounded so that they could treat themselves; and “mercy dogs” would stay with dying soldiers to keep them company. Such stories bear witness to the loyalty of animals. Dick, a black retriever messenger dog, was wounded in action but recovered enough to resume his duties. He developed a limp, grew weaker, and had to be put down. A postmortem showed that he’d been working with a bullet lodged in his chest and a shell splinter close to his spine.

Other animals acted as canaries in the mine. One South African unit had a baboon called Jackie with sharp hearing, who would tug at men’s sleeves if he detected enemy advances. Slugs were used when it was discovered they would visibly demonstrate their discomfort in the presence of mustard gas in smaller quantities than humans could sense, allowing soldiers to don their gas masks in time.

Around 100,000 pigeons served, too. One delivered a message from a US battalion trapped behind enemy lines: “Our artillery is dropping a barrage directly on us. For heaven’s sake stop it”. The birds’ work was so important that they were protected by the Defence of the Realm Act, which criminalised any attempt to kill or maltreat them. It was an ironic implementation of animal rights to mirror the first conservation law in Britain, introduced by the 8th century saint, Cuthbert, who declared that the eider ducks of the Farne Islands should be protected; ironic because during the war, huge rafts of eiders at rest in the North Sea were used by the RAF for target practice.

Whales were used for the same purpose. It was the first time cetaceans had been seen and photographed from the air. One account noted, “In the half-lights, these huge monsters bore a strong resemblance to a submerged U-boat, and, as the rule in war was, ‘When in doubt, bomb’, a good many of them were killed by our aircraft.” Meanwhile, 175,000 whales died in the South Atlantic to furnish rifle oil, fuel for trench stoves and oil to protect against trench foot. Germany culled dolphins and seals for their oil.

Whales were also co-opted to deal with food shortages: as Michael Freemantle notes in his book The Chemists’ War, Lever Brothers had worked out how to hydrogenate whale oil to make it fit for human consumption. Most terribly, these placid animals were processed into munitions themselves as their bodies yielded glycerine for bombs.

The British cavalry passing the remains of Albert Cathedral, after the second Battle of the Somme, August 1918. Photograph: Hulton Archive/Getty Images

It wouldn’t be until later in the century that humans employed cetaceans in war, but even in the postwar period, consciences were stirring. In a 1924 essay entitled The Impudence of Flags: Our Power Resources and My Elephants, Whales and Gorillas, HG Wells, prophetic author of The War of the Worlds, wrote: “The dwindling world fauna of this planet is in urgent need of international game laws and a supernational game-keeper. Species of whales are being exterminated because the ocean is no man’s land.”

In the fitful periods of peace in the last century, there was no armistice for animals, and monuments to their efforts are few, London’s Park Lane memorial being a noble exception. One hundred years after the first war of the anthropocene, itself a perversion of nature and fought for the Earth’s resources, these non-human casualties remain as an indelible stain on our conscience.